Re: FW: XFree86 future

On Sun, Mar 23, 2003 at 10:35:19AM +0100, Lukas Molzberger wrote:
> > Don't worry, we're not planning on getting rid of the client-server
> >model any time soon.  David Wexelblat is correct in the sense that 
> >the majority of people do not need it, but it's definitely the case 
> >that some people find it essential.  Not only that, I disagree with him.
> >I think direct rendered 2D has little to no benefit.
> >
> >
> >                        Mark.
> 
> If direct rendered 2D would bring little to no benefit why then is the 
> performance of direct rendered 3D under XFree so much better than the 2D 

How can you compare them ? They have very little in common, and
performance bottleneck are very different. In 3D basically you just
upload textures and vertices to the graphic core, and the graphic core
handles all the rest of it. In 2D, for the currently accelerated part i
think you cannot really pry anymore performance out of the current
hardware, except maybe by using the dma engine instead of mmio register
access, but i have heard that it doesn't give much better performance
(because of the overhead of the dma engine), but the radeon driver
already does so, and i guess that it much depends on the graphic
hardware.

Now, the slowness probably is about the RENDER extention, where you have
to move huge chunks of pixmaps and alpha masks around, and which is not
hardware accelerated in the most case (apart from the mga driver and the
XIG Server apparently). I feel that the cause of this is because moving
pixmaps around over the network cannot be good performance, unless you
have a faster network than you have a processor or graphic card. The
correct solution to this is to use vector graphics, as Apple did do, and
is in the pipe for X 5.0, and the new SVG graphics support in gnome is
also a good step to there, altough i have the feeling that this
developpment is years late, but then i am not familiar with the reason
for it. 

That said, if 3D is really all that faster, i hear that OpenGL has also
a nice 2D API that could be used.

One thing that would be nice is to have a common driver for 2D and 3D.
Or at least that both use the same command stream (the drm dma engine if
it is available, mmios if not, altough there is no 3D anyway in this
last case). Context switching and chip synchronization are expensive
operations and maybe responsible for poor performance.

> performance. Many people argued that the device drivers are to blame for the 
> bad 2D performance but I would think that it is a much harder problem to get 

Well, 2D performance is mostly about moving pixels around, and you can
do that only as fast as the hardware allows. Now the RENDER extension is
currently unaccelerated, is in part because each time i asked Keith
about information on how to accelerate it, he responded there is no doc
(yet) and RENDER is not really ready, stable, etc, so he would not write
such documentation. If he responded at all, that is. I asked him on and
off about this in the past two years, and got this selfsame reply last
around last october or such.

> the 3D part of the graphics driver right than it is to get the 2D part right. 
> I'm certain that network transparency together with the ancient X11 API's are 
> a large part of the problem of the XFree project. I've worked on several 

Well, on local X, the network part is supposed to be almost transparent
and cost very little, so why remove it.

Friendly,

Sven Luther